1. Field of the Invention
The present invention relates to a pigment dispersion liquid having excellent dispersion stability of pigment, a curable composition which is obtained by using the same and which is suitable for preparing a color filter to be used for a liquid crystal display (LCD), a solid state imaging device (for example, a CCD or CMOS) or the like, a color filer having a colored pattern formed from the curable composition, and a solid state imaging device.
2. Description of the Related Art
A color filer is an indispensable constitutional component in a liquid crystal display or a solid state imaging device.
In comparison with a display using a cathode ray tube (CRT: Braun tube) as a display device, a liquid crystal display (LCD) is compact and has an equal or higher performance. Therefore, LCDs have come to be the mainstream for television screens, personal computer screens and other display apparatus. Also, in recent years, the trend in development of liquid crystal displays is moving, from conventional monitor applications in which the screen has a relatively small area, toward TV applications in which the screen is large and a high image quality is required.
In the field of color filters for liquid crystal displays, the substrate size is enlarged in order to produce a large-sized TV, and curing with low energy is desired for the purpose of improving the productivity when using a large-sized substrate. Also, in the field of liquid crystal displays for TVs, a higher image quality is required as compared with that for a conventional monitor. That is, improvements in contrast and color purity are required. For the purpose of improving the contrast, with respect to a curable composition to be used in the preparation of a color filter, a finer particle size is required for a coloring agent (for example, organic pigments) to be used (see, for example, JP-A No. 2006-30541). Accompanying this, the addition amount of a dispersant for dispersing a pigment tends to increase. Also, for the purpose of improving the color purity, a higher content of a coloring agent (for example, organic pigments) in the solid content of the curable composition is required. Accordingly, the contents of a photopolymerization initiator and a photopolymerizable monomer in the solid content of the curable composition tend to decrease.
On the other hand, curing with low energy is also desired in the field of color filters for solid state imaging devices. Also, production of thinner patterns is advancing, and accompanying this, the concentration of a pigment in the composition is increasing. Furthermore, in a pigment type color filter, along with the use of a small particle size pigment, a proportion of a pigment dispersant in the composition tends to increase.
Also, in order to deal with a problem such as color unevenness, which is caused since the pigment has relatively coarse particles, a technology has been proposed which uses an organic solvent-soluble dye as the coloring agent in place of the pigment (see, for example, JP-A No. 2-127602). However, there are cases where the dye exhibits a polymerization inhibition effect derived from its structure. In a color filter in which a dye is used as a coloring agent, since the concentration of the dye increases, the problem of the polymerization inhibition effect derived from the dye becomes remarkable, and it is difficult to realize a high density colored layer using a dye.
Accompanying thinning of the colored layer, the content ratios of a coloring agent in a curable composition for forming the colored layer, namely a pigment and a pigment dispersant, increase, whereas the content ratios of curing components (a polymerizable component and a polymerization initiator) become relatively low. Accordingly, there is a problem generated in that the sensitivity cannot be sufficiently secured. Also, the addition amounts of a polymer having a high acid value, a development accelerator and the like to be added to the curable composition for the purpose of securing developability relatively decrease, and therefore, there is apprehension that defective development is caused.
As described above, in the case where sufficient curability and developability are not obtained, the colored pattern forming properties are lowered, and the performance of the obtained color filter is reduced. This problem is remarkable in a solid state imaging device which is required to have fine pattern forming properties.
For the purpose of securing sensitivity and developability, it is desired to decrease the ratios of a pigment and a pigment dispersant. However, in order to achieve desired color value and spectral characteristics, it is not preferable to decrease the content of the pigment, and it is being attempted to decrease the amount of the pigment dispersant. However, in general, when the amount of the dispersant is decreased, sufficient dispersion stability of pigment is not obtained, resulting in a problem in that an increase in viscosity is caused over time.
In particular, in a pigment having a barbituric skeleton, such as yellow pigments, a decrease in dispersion stability of pigment over time is remarkable, and it is the present state that a pigment dispersion liquid which is able to achieve stable dispersion with a small amount of a dispersant is required.
As described above, in order to realize a colored pattern having a sufficient color forming property even in a thin layer, a colored curable composition is earnestly desired which has excellent pattern forming properties such as sensitivity and developability even in the case where a coloring agent is contained in a high concentration.